The present invention relates to ester compounds derived from 3,4,5-trimethoxy phenyl acetate, 3,4,5-trimethoxy cinnamate or 3,4,5-trimethoxy hydrocinnamate that are represented by Formula (I), wherein R.sub.1 is CH.sub.2--, --CH.dbd.CH-- or CH.sub.2--CH.sub.2, R.sub.2 is thymyl or carvacryl, to methods for preparing them, and to a whitening cosmetic composition containing the ester compounds. Because the ester compounds of the present invention inhibit the generation of melanin, the cosmetic composition can improve the skin pigmentation and can be used for whitening cosmetics.